Method of making laminated structures



Feb. 12, 1946. E. L. VIDAL ETAL METHODS OF MAKING LAMINATED STRUCTURES Original Filed Sept. '12, 1940 5 Sheets-Sheet l HH l lh lHF INVENTORS 41 XTVM 4M BY 5 A ZATTONEYM- Feb. 12, 1946. E. VIDAL ETIAL 2,394,730

METHODS OF MAKII ING LAMINATED STRUCTURES Original Filed Sept 12, 194 0 5 Sheets-Sheet 2 I I f g 7 I I I H 11 1 W w \x\\&\ La Pics.

INVENTORS Kym! Md BY u Feb. 12, 1946.

O'riginal Filed Sept. 12, 1940 5 Sheets-Sheet 3 INVENTORS p a Vale M Feb. 12, 1946. E, WDAL ET A; 2,394,730

METHODS OF MAKING LAMINATED STRUCTURES Original Filed Sept. 12, 1940 S'Sheets-Sheei; 4

INVENTORS Feb. 12, 1946. E. VlDAL in A1. 2,394,730

METHODS OF MAKING LAMINATED STRUCTURES Original Filed Sept. 12, 1940 5 SheetsTSheet 5 Patented F eb. 12, 1946 UNITED STATE METHOD S PATENT OFFICE or MAKING LAMINATE STRUCTURES Eugene L. Vidal, Washington, D. a... Laurence J. Marhoefer, Haddon Heights, N. J .,-assignors to Vidal Corporation, Camden, N. 1., a corporation of Delaware Original application September 12, 1940, Serial Divided and this application November 11, 1943, Serial No. 509,845

1 Claim.

This invention relates to structures fabricated from laminations of adhesively treated material and to methods 01' making such structures.

ribs and longitudinal spars must be firstassembled and thereafter sections of the skin sepathat the thin skin is of a material requiring carenu attention during fabrication and skilled workmanship during assembly. v Accordingly, it is an object of the present invention to provide a "tures, such as aircraft wings, said structures having a high strength-to-weight ratio.

Another object is to provide a novel method whereby parts of an aircraft wing can be fabricated on inexpensive molds.

A further object is to provide a novel method of reinforcing structures fabricated in accordance with the above method.

Still another object is to provide a novel method of fabricating the entire shell of a hollow, elongated member, such as a'fiap or aileron, in a single molding operation.

A still further object is to provide a novel laminated airfoil having reinforcing members novelly secured to the skin thereof.

Another object is to provide a novel method for eliminating surface irregularities in a reinforced molded structure without decreasing the strength of said structure.

A still further-object is to form in a novel manner the framework and skin of an airfoil.

' The above and other objects and novel features of this invention will more fully appear from the following detailed description when the latter is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention, reference being primarily had for this latter purpose to the appended claim.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

Fig. 1 is a top plan view of an airplane wing rately applied to said framework and to the fact fabricated according to the method of the present invention;

Fig. 2 is a sectional view taken substantially along line 2- 2 of. Fig. 1;

Fig. 3 is a fragmentary sectional'view of a reinforcing member located in a mold and the manner of superposing skin laminations on said mold over said member; a

Fig. 4 is a view similar to Fig. 3, showing the above parts after molding; I

Fig. 5 is a sectional view taken along line 55 of Fig. 1 showing one type of attachment for securing wing sections to each other;

Fig. 6 is a perspective view of a portion of a type of mold .or form on which the central part of the wing of Fig. 1 may be fabricated;

Fig. '7 is an exploded perspective view showing the parts comprising the framework of awing section;

Fig. 8 is a perspective view showing the parts of the wing section assembled on the mold of Fig. 6;

Fig. 91s a perspective view of a fragment of the molded section; r

Fig. 10 isa view in side elevation with par broken away of the mold of Fig. 6;

Fig. 11 is a sectional-view taken along line 'll-ll of Fig. 1 showing another section of the wins;

Fig. 12 is a view, in perspective of a portion of a mold upon which the wing section of Fig. 11 may be formed;

Fig. 13 is an exploded perspective view of a portion of the mold of Fig. 12 and of a preformed mold upon which a trailing section of the wing may be formed;

Fig. 17 is a perspective view of a segment of said trailing section;

F 18 is a perspective view of a mold upon which an aileron may be fabricated;

away of the mold of Fig. 18 with laminations assembled thereon and molded, said view being taken substantially along line l9-l9 of Fig. 18;

Fig. 19A is a view in sectional elevation of the completed aileron of Fig. 19 taken along a Fig. 19 is a perspective view with parts broken line corresponding to the line, IO-l! of Fig. 18.

Fig. 20 is a top plan view of a mold for carrying out the fabrication of another embodiment of a wing section, such as an aileron;

, Fig. 21 is a sectional view taken along line 2l-2I of Fig. 20, with a laminated structure assembled on the mold;

Fig. 22 is a perspective view with parts broken away of a portion of the aileron formed on the mold of Fig. 20;

Fig. 23 is a view in side elevationof a mold on which the leading edge of the wing of Fig. 1 may be formed;

Fig. 24 is a sectional view taken substantially along line 24-24 of Fig. 23;

Fig. 25 is a sectional view taken substantially along line 25-25 of Fig. 23;

Fig. 26 is a view in perspective of a preformed rib member adapted to constitute a part of the framework of the nose section; V

Fig. 27 is a similar view to Fig. 25 with the rib member of Fig. 26 positioned for molding;

Fig. 28 is a perspective view of a portion of the nosesection;

Fig. 29 is a top plan view of a mold for forming a section of the wing tip;

Fig. 30 is a similar view of a mold for forming another section of said tip; and

Fig. 31 is an exploded view of the several part of the wing tip.

According to the novel method comprehended by the present invention, a structural member, such as an aircraft wing, s novelly formed in one or more sections from a plurality of adhesively treated laminations of a material such as wood veneer. The laminations are shaped and bonded together by a molding operation which preferably includes the application of heat and fluid pressure but which may be accomplished by the application of pressure, only. The molded to season for several hoursand then if a more time, and in the event molded structures are to be Joined to each other by a further molding 1 operation, said molded structures have to be retreated with adhesive at their junctions.

The adhesive is applied to the sheets, prefer;

ably in a sufficient quantity to impregnate and coat the same in any suitable manner, as, for example, by being sprayed or painted thereon or by dipping the sheets in the adhesive. After the adhesive is applied, the sheets are permitted thorough impregnation and coating is desired the application of the adhesive and the seasoning are repeated one or more times. In the fabricationof a structure having curved surfaces from sheets impregnatedvvith a thermoplastic, it is preferable to mix a plasticizer, such as dibutyl phthalate, with the adhesive in sufficient sections are removed from the mold and joined together to form the complete wing structure either mechanically or by a local molding carried out by mechanical presses.

The veneer sheets which are utilized to carry out the method have a thickness which depends onthe desired weight, thickness and structural strength of the member being formed therefrom,

for example, when a member having a high strength-to-weight ratio is to be formed, thin sheets from $4,, to 54;" are used ina sufllcient number of layers to give the requisite strength, whereas toform a thick structure requiring little shaping it is satisfactory to employ sheets having a thickness of A" or more. In the fabrication of aircraft parts, such as wings, weight must be maintained at a minimum and, accordingly, thin sheets are used. Furthermore, although solid strips could be used as reinforcing or frame members, it is preferable first to form said strips and other reinforcing members from veneer laminations, a plurality of said members, wherever possible, being molded by the same molding method as a block from which block the members are sawed or otherwise removed.

The sheets of material are treated with a suitable adhesive, preferably of the thermoplastic or thermosetting group, as, for example, polyvinyl butyral. It is also possible to employ other adhesives, for example, of the type adapted to be set by chemical reaction and requiring the application of pressure only during molding, such as urea formaldehyde. The use of the latter type of adhesive is somewhat less satisfactory because the initial molding requires more care and quantity to make the impregnated sheets sufficiently flexible to enable them to conform substantially to the curved surface, the quantity of plasticizer added to the thermoplastic varying inversely as the radius of curvature of the shape into which the veneer sheets are to be formed.

The novel aircraft wing fabricated according to the novel method of the present invention comprises a beam section 40 (Fig. 1) located intermediate the leading and trailing edges of the wing and extending longitudinally, i. e., in the direction of the wing span, for almost the entire length of said span, said beam section constituting the main supportfor the wing. A leading edge or nose section 4| is secured to the forward edge of beam section 4|] and trailing edge or tail sections 42 and 43are secured to the rear edge of said beam section, trailing edge section 42 having a flap 44 hinged thereon, and section' 43 having an aileron 45 associated therewith. A separate tip section 46 isalso provided and is adapted to be secured to the end of beam section 40 and to constitute the tip of the wing.

Beam section 40 is formed on a mold 41 .(Fig. 6)

provided with transverse recesses 48 located where reinforcing frames for the beam are desired and longitudinal grooves or recesses 49 which inter I sect said transverse recesses and extend substantially the length of the beam, the spacing of recesses 48 and and the length of'the latter recesses being determined by the desired strength and rigidity of the beam section. Mold 4! is provided with rounded edges'and has an indentation or recess 50 at each of said edges and is prefer: I

. .and 52 (Fig. 7), corner pieces 53 and side pieces 54, said frame members being recessed so as to interlock with strips 55 which are adapted to fill grooves 49 and which are also recessed. Indentations 50 at each edge of mold 41 are filled with arcuate strips 58 which preferably extend the length of said mold and a filler strip 59 to "square ofi the edges is provided at each of the mold edges being positioned over each of said arcuate strips. It is preferable to provide a side rein forcing strip between each pair of transverse frames and grooves 56 (Figs. 6 and 10) are provided for this purpose in order to receive side I pieces 51 (Fig. 9).

Thereafter, a plurality of adhesively treated sheets of veneer 60 are superposed on the four sides of mold 41 and are temporarily secured to the mold by any suitable means, such as cleats or belts (not shown). of the veneer layers may progressively diminish toward the beam tip, 1. e., some of the layers may terminate at a predetermined distance from the tip. In order to further strengthen the broad end of beam section. 40, an internal flange of sheets of veneer is built up by providing adepressed portion 6| in the end of mold 41 which may be filled with veneer strips 8 I a before veneer sheets 60 are positioned.

/ When the above-described structure is proper-' ly assembled on the mold in the above-described manner and theexposed surfaces are rendered non-adhesive, for example, by being coated with cellulose acetate, the assembly and the mold are subjected to a, molding operation which includes the application of pressure whereby the laminations are caused to closely conform to the mold shape while the adhesive is actuated and caused to set. This is preferably accomplished by inserting the mold and the assembly thereon into a flexible, substantially impervious container and then placing said container into a pressure cham- The aggregate thickness her wherein'said container is preferably subjected to fluid pressure. The interior of the container is in communication with the exterior of the chamber so that the pressure in the latter will I exhaust said container and cause the walls thereheat is desired for activating the adhesive. The

pressure remains applied until the adhesive has set and then the mold and the structure molded thereon are removed from the chamber and from the container.

Heretofore the fabrication of reinforced laminated structures on molds has resulted in the production of either ridges or hollows in the skin of the structure due to the irregularities in the thickness of the reinforcing members which either fail to fill or project beyond the grooves provided therefor. To overcome this defect without decreasing the skin strength in the products of the present invention, it is proposed to locate one or more extra strips 62 (Figs. 3 and 4) of laminated material over the top lamination at each of the grooves containing reinforcing members and to use reinforcing members which are some what undersized, said strips being of a width substantially equal to or slightly greater thanthe width of said grooves. As a result, when the structure is molded, although a hollow is provided in the skin of the structure, this hollow is filled with these extra laminations. Theportion of the latter which projects beyond the skin surface is thereafter removeed without decreasing the skin strength and this removal can be readily accomplished, for example, by a sand-papering machine. The foregoing feature of this inventionis claimed in our copending application Serial No. 593,840, filed May 15, 1945.

After beam section has been molded and the mold removed, one or more of the transverse by a routing machine, in the upper and lower .faces of said beam section adjacent each edge It will be understood that these W of the latter. recesses could also be produced b having outer laminations of a lesser width covering the upper and lower faces of the beam section, said outer laminations being centrally located relative to the others.

Trailing section 42 to which flap 44 is. hingedly secured (Fig. 11) is formed together with its reinforcing webs or ribs 68 upon a mold 81 (Fig. 12) As shown, the latter comprises a base portion 68 and a plurality of similarly shaped sections 83, each of which consists of two parts 69a and 69b, the latter mold part (Fig. 13) having one face thereof conforming to one side of rib 66 and having slots I0 located in said face to receive stiffeners II, which are preferably formed with said rib. A plurality of recesses I! exist between 'mold parts 69a and 69b of adjacent sections 69 and each of said recesses is adapted to receve the web 13 of one of ribs 66. Indentations I4 are provided in, the sides of each of mold'parts 69b in order to receive flanges 15 of said ribs and strips 16 are provided to fill in the spaces which exist between the rounded edges of said ribs and parts 69a. With rib assembly 66,18 properly positioned on mold 61 and a strip 11 located at the tip of said mold and extending along thelength thereof, skin laminations are superposed on the mold faces, flanges 18 of the ribs 'which are substantially flush with the faces of the mold being engaged by said skin laminations. Laminations 18 (Figs. '11 and 15) corresponding to the upper skin are positioned so as to cover the entire face of the mold, whereas laminations 19 which form the lower skin cover only the portion of the mold face, as shown in Fig. 12, below in order to form a'space 8| in trailing section 42 which is adapted to receive flap The mold and the assembly thereon are then subjected to the steps of a molding process similar to that carried out in order to mold section 40 and thereafter a beam 82 is positioned between the rearmost portion of skin 19 and ribs 66 and provides a support to which one side of a hinge 88 is secured by suitable means, such as screws (not shown). The portions of the skin I8, 19 of section 42 (Fig. .11) which extend beyond the end of ribs 66, i. e., the portions of the skin laminations molded on base 68, are adapted to overlap beam section 40 and fit into recesses 65, said portions being secured to said beam section by being molded thereto, as, for example, by a mechanical press P having a heating coil C associated therewith.

Flap 44 is preferably formed ona mold 85 which provides for the positioning of reinforcing members 86 at the trailing edge of said flap, said members being molded together with and therefore bonded to skin laminations 81 which are superposed on both sides of the mold. A U- shaped member 88 (Fig. 15) extending the length of said flap and preferably premolded to the desired shape from a plurality of adhesively treated laminations is located between the sides 81 of said flap at the leading edge thereof, said mem. her being adhesively secured to said sides, for example, by' a heating press. Flap 44 is then attached to the free side of hinge 83 and is controlled by means well-known in the art, openings a being provided in ribs 60 topermit said control means to extend through trailing section 42. Flap 44 may be formed with skin laminations on the lower side thereof only, i.-e., skin laminations 1 TI are superposed only on one side of mold 85 1 prior to molding.

Trailing section 43 is formed on a mold 89, the latter comprising an assembly of sections substantially similar to the sections constitutingedges of the portion of said mold corresponding to the trailing edge and filler strips, not shown, similar to strips I of trailing section 42 areprovided for the same purpose as the latter strips.

Thereafter, skin laminations 95 are positioned on three sides of said mold and the entire mold assembly molded into 'the structural unit (Fig. 17)

which constitutes trailing section 43. The mold is then removed from said unit and thelatter is preferably secured to beam section 40 by the application of heat and pressure which bonds skin 95 to the upper and lower surfaces of section 40 along recesses 65 (Fig. 2).

Aileron 45, which is associated with trailing section 43, being pivotallymounted to the rear thereof, is formed in a novel manner on a mold '95 (Fig. 18), the latter being shaped to conform to the interior of said aileron and being provided on both sides with a. plurality of grooves 91, each of which extends from the trailing edge to within a short distance of the leading edge of said mold. Grooves 91 are preferably flared at each end and the group of said grooves on the top side of mold 96 is adapted to receive reinforcin members 900. (Fig. 19) while the grooves on the bottom side receive members 98b, said members being shaped to fit said grooves. The thickness of said members is greater thanthe depth of said grooves, except for the portions thereof which are overlapped by laminations 99, the latter being positioned to cover'the leading edge of said mold. By varying the thickness of members 98a and 98b in this manner, the joint between said members and laminations 99 produces a smooth outer surface over which additional veneer laminations may be positioned to constitute the skin of said aileron when molded. However, in order to balance the aileron and properly locate the I center of gravity thereof, it is preferable that members 98a and 98b be covered with a fabric, such as canvas. The canvas by being treated with adhesive may be molded together with laminations 99 and members 98a, 98b in a single molding operation of the kind hereinafter described, but is preferably attached to said lami- I nations and members by means of an adhesive 0 after the latter have been molded. Accordin ly. after said laminations and members are positioned on mold 96, the same are subjected to a molding process and bonded into a structural 98a and 9812 from said mold, thus separating the two sides of the molded structure and permitting the withdrawal of the mold from the rear of said structure, the latter being sufilciently rerality of adhesively treated elements, all of the parts of said member being bonded to each other except along a single line extending the length of members 98a, 99b, and a U-shaped reinforc ing piec'e IN i preferably fixed between the 4 ends of leading edge '99. Canvas skin I02 is positioned over framework 98a, 98b, 99 to complete the aileron structure.

Another aileron embodiment I .II (Figs. 21, 22)

may be formed upon a mold I03 (Fig. the latter comprising'a nose portion I04 which is indented relative to atrailing'portion I05 which has a-plurality of angularly disposed grooves I08 I ing operation and after fabrication the two sides of the skin are separated to permitthe removal of the mold. Strips II 0 are then bonded together to complete the formation'of airfoil section III.

The nose or leading edge portion .4I of the 'wing is fabricated on a mold II2 comprising a tip portion II3, a base H4 and a plurality of sections II 5 located between said tip and. base parts H50; and H51). Sections II5 are positioned so as to produce a plurality of recesses I I1 therebetween and said recesses are adapted to receive a plurality of ribs IIIi (Fig. 26).

A selected number of said ribs may be provided with stiifeners II8 (Fig. 26) and in the illustrated embodiment alternate ribs are so provided and, accordingly, alternate sections II5 are provided with slots 9 to receiye said stifleners. Filler strips I20 are utilized in a manner hereinbeforedescribed to fill the groove remaining in the mold faces after the positioning of ribs II6 (Fig. 27). Thereafter a formed arcuate tip or nose piece I2I of a length equal to the length of leading edge section 4I is'positioned a a single piece or in sections on mold II2 to cover tip portion I I3 of said mold. -It is to be understood that instead of separately molding nose piece I2I, the

-latter may be formed simultaneously with the 5 skin of. section M by superposing a plurality of adhesively treated sheets over said tip portion of the mold. The mold is then'covered with veneer laminations I22 and all the parts assembled on the mold are bonded into a unitary structure (Fig.

7 28). This structur which constitutes nose section M of the wing is then adhesively secured to leading edge of beam section 40 (Figs. 1 and 2), preferably by means of a mechanicalpress in the same manner as trailing section 42 is secured to' the trailing edge of said beam.

og said mold. After the removal of mold 99. a strip I00 is adhesively secured to the free ends tire airfoil structure is-formed in a single .moldportions, each of said sections consisting of two 4 asomso an integral part of the main .wing section, fabrl- 5 cated and molded at the same time. As shown. said tip section comprises a leading portion a, a traling portionlfib and a beam or central portion a to which said two first-named portions are adhesively attached. Trailing portion lib 1 is formed on a mold I23 (Fig. '29), said mold comprising sections I24 having recesses i241: therebetween adapted to receive reinforcing ribs If and an edge section I," adapted to position the laminations comprising an edge reinforcing l8 strip I 21, said edge section being preferably formed in several parts to facilitate the removal. I

thereof from the structure molded thereon. A base section I28 is. also a part of said mold and the portions of skin laminations' |2O which cover said base section constitute the skin portions which are attached to central 'sectiorrllc, the latter being readily formed, for example, on a simple mold.

The leading portion a is formed on a mold I30 which although shaped differently is constituted of a plurality of parts which are essentially like those of mold I23, producing a laminated I structure having a skin I31 ofthe desired shape and being provided with a reinforcing strip I32 30 and ribs I33. Portion a is attached to central section c in the same way as section b and the resulting structure'is-secured to the wing, preferably by mechanical means. This is accomplished by mechanically or adhesively attaching 35 a flange IN on the interior of beam- I along the edge thereof adjacent tip 48 andlikewise providing a flange l35-on central section lie of said tip (Fig. 5), said flanges being rigidly fixed to each other by suitable means, such as bolts. Ill.

During or after the assembly or the wing, it

may be desirable to reach into the interior thereof, for example, in order to secure tip 46 in position or to locate and attach the flap and aileron ricating a wing for an aircraft, said wing being I comprised of. a plurality of novel molded sections which may be adhesively and/or mechanically secured to each other.

There is also provided a novel method of fabricating an elongated shell structure; such as an aileron. in a single molding op ration and a novel method whereby a smooth skin is provided onan airfoil wing even though said wing. is molded from laminations of adhesively treated materials and is provided with adhesively secured reinforcing members. a

The present invention is a division of our copending application Serial No. 356,426, tlledBeptember 12, 1940, now issued as Patent No. 2,348,316, dated May 9, 1944.

Although only a single embodiment of th invention has been illustrated and described, it is g to be expressly understood that the samelis not limited thereto. For example, it will'now be apparent that a central section of similar construction and fabricated by the same method as the- "above-described win! panels may be attached thereto to form a complete wing. Furthermore. the main beam of said central sectionor of said panelsmay be partitioned oi! to be used as a gas tank. various other changes may be made in the design and arrangement or parts without departing from the spirit and scope of the invention. For a'deflnition of the invention --reference will be had primarily to the appended Whatisclaimed is:

' A method of making an airfoil member which consists .in providing a mold conforming to the interior of said member, positioning adhesively treated reinforcing strips in groovesprovided in said mold, superposing laminatibns of adhesively treated material on the mold exterior, the portions of the laminations covering one side of the mold being separated at the trailingedge of the airfoil member from the portions. of the laminations covering the other side of the mold. subjecting the assembly on the mold to a molding process whereby said laminations and strips controls, and for this purpose'a plurality of conveniently located hand openings I31, the veneer are bonded together, freeing the upper and lower -molded sides of said assembly from the. mold by apart said-sides at the trailingedge, removing the mold through'the opening thus formed,',and permanently Joining said sides at the trailing edge.

- EUGENE L. VIDAL.

LAURENCE J. MARHOEF ER. 

